The invention relates to a picture scanning and recording method and an apparatus for carrying out the method. More particularly, the invention relates to a system and a method including two scanning beams having different sizes of focused areas which are alternately projected in principal scan directions upon an original picture to be duplicated. The two scanning beams produce "sharp" signals (raw image signals) and "unsharp" signals that in turn are processed with each other to form a series of final image signals which have detail emphasizing components in accordance with the detail portions of said original picture, whereby the image signals serve to control recording or exposing beam so as to produce highly contrasted duplicates.
In said system, it is popular to move the original picture in a subordinate direction at right angles to the principal scanning direction such that the scanning beams are switched over one to another at the ends of forward and backward scan passages respectively adapted to produce series of "sharp" signals and "unsharp" signals or vice versa.
There are two known methods in relation to the above system. One of the known methods as disclosed in U.S. Pat. No. 4,080,634 utilizes a common photosensor to detect optical signals and produce the electric raw image signals (hereinafter called "sharp" signals) and "unsharp" signals. However, use of a The single photosensor makes it necessary to modify one of the scanning beams in order to separately sense optical signals produced by these two beams. The modified and unmodified beams are arranged to have the same optical axis. These beams of scanning light are reflected by or transmitted through the optical picture and detected by the single common photosensor. One series of detected signals originating from the modified beam are then processed in a demodulation device so that they can normally be compared with the other series of signals originating from the unmodified beam. It is however impossible to separate with an absolute correctness the two series of said signals, even if the demodulation was conducted with the highest possible accuracy. Moreover, as devices are developed which scan at increasingly faster speeds, it will become more difficult to accurately modify the scanning beam at a speed higher than that of detection and electronic processing of detected data.
In the other known method, individual photosensors are used, respectively, for the "sharp" and "unsharp" signals. Scanning light beams having different wave lengths are used to produce these two signals according to a proposed technique disclosed in Japanese Examined Publication Gazette (Patent) No. Sho. 54-22122 in the name of the applicant of the present application. For example, a red light is assigned to the "sharp" signals and a blue light is assigned to the "unsharp" signals. The photosensors are provided with proper filters to detect only the scanning beams with the assigned colors. This technique, which is free from the problems inevitable in the first known method, is, however, not available for a polychromatic original picture because red or blue portions thereof are very likely to produce detail emphasizing signals ("unsharp mask signals") despite a lack of variance in brightness at or adjacent said portions. Additional drawbacks of the above technique are a difficulty in balancing the sensitivities of the dual photosensors and a complicated structure for accommodation of two sources of light and two photosensors.
The applicant has proposed a third method described in Japanese Early Publication Gazette (Patent) Sho. No. 56-8140, which corresponds to U.S. Pat. No. 4,319,268, where the detail emphasizing signals are produced by digitally processing relevant data. This system requires a memory capable of storing a large number of signals corresponding to the pictorial elements in the line being scanned and in plural adjacent scanning lines. This System also requires a complicated electronic circuit to perform digital computations for each of the numerous pictorial elements that are to constitute a duplicated picture.
It is therefore an object of the invention to provide a picture scanning and recording method and apparatus which are free from the aforementioned disadvantages of the known methods.
In particular, another object of the invention is to provide such a method and an apparatus for producing two series of signals, e.g. "sharp" signals and "unsharp" signals, by alternately scanning an original picture by means of different beams of light or laser in alternate half periods of each scanning period, temporarily storing the preceding series of said signals, e.g. "sharp" or "unsharp" signals, in a memory to thereafter be retrieved for synchronized processing with the following series of signals, e.g. "unsharp" or "sharp" signals.
According to the invention, the scanning beams have different sizes of focused areas on the picture and are adapted to be detected by a single common photoelectric converter when advancing along principal scan passages at different time periods determined by switching in the principal scan direction or by a preset displacement in the subordinate scan direction. A series of final image signals, computed from the above signals, serve to control an exposing or recording scan beam which produces a duplicated picture with a high contrast.
The invention, by utilizing a single photoelectric converter to produce during different time periods two series of signals capable of being synchronized, eliminates the possibility of inconformity or distortion in detail emphasizing signals. In short, the invention advantageously provides duplicated pictures of good quality and utilizes a simpler scanning structure than prior art devices.
Other objects and advantages of the invention will become clear in the following description of a preferred embodiment shown in the drawings.